1. Field of the Invention
The present invention relates to an ink composition and an inkjet recording method, and more particularly, it relates to an ink composition and an inkjet recording method capable of fixing an image with high quality to a recording medium at a low temperature and a high speed.
2. Description of the Related Art
As an image recording process of forming an image on a recording material, such as paper, based on image data signals, the electrophotographic system, the sublimation or melting thermal transfer system and the inkjet system have been conventionally known. Among these, the electrophotographic system requires such a process that an electrostatic latent image is formed on a photoreceptor drum through charging or exposure to necessitate a complex system, and an apparatus therefor is expensive. The thermal transfer system involves a high running cost and problems, such as formation of waste materials, due to the use of an ink ribbon, although an apparatus therefor itself is inexpensive in comparison to the electrophotographic system. In the inkjet system, on the other hand, image formation is carried out with an inexpensive apparatus in such a manner that an ink is ejected directly to only a necessary image part on a recording material, and thereby the ink can be used efficiently to reduce the running cost. Furthermore, the inkjet system causes less noise, and is excellent as an image recording process.
The inkjet recording system includes, for example, a system of flying ink droplets by pressure of vapor generated by heat from a heater, a system of flying ink droplets by mechanical pressure pulses generated by a piezoelectric element, and a system of flying ink droplets containing charged particles by utilizing an electrostatic field (as described in Japanese Patent No. 3,315,334 and U.S. Pat. No. 6,158,844). The system of flying ink droplets with vapor or mechanical pressure cannot control the flying direction of ink droplets, and there are some cases where ink droplets are difficult to be attached accurately to desired positions on a printing media due to distortion of ink nozzles and air convection.
On the other hand, the system utilizing an electrostatic field controls the flying direction of ink droplets with the electrostatic field to enable ink droplets to be attached desired positions, and thus has advantages that an imaged material (printed matter) with high image quality can be produced.
As an ink composition used for the inkjet recording system utilizing an electrostatic field, an ink composition containing charged particles containing at least a colorant is generally employed (as described in JP-A-8-291267 and U.S. Pat. No. 5,952,048). The ink composition containing a colorant can be formed as inks of four colors, i.e., yellow, magenta, cyan and black, by changing the colorant, and can also be formed as special color inks of gold and silver. Accordingly, the ink composition is useful for producing a color imaged material (printed matter) In order to maintain the high image quality and to produce color imaged materials (printed matters) stably, it is necessary to provide means for fixing the ink composition to paper. In the inkjet recording system, furthermore, the fixation is attained without deterioration of image quality at a low temperature with high speed under such conditions that a solvent remains in the image part and the paper, and the fixation satisfying the all the aforementioned requirements has not yet been realized.